Backplanes are printed circuit boards or metal plates on the upper side of which "daughter" PCBs are detachably mounted perpendicularly to the backplanes for easy removal. One way of electrically connecting the daughter boards to other daughter boards, the backplane, and other circuitry is by providing metallized surface portions near the edges of the daughter boards and inserting them between the forked prongs of electrical connectors that are secured to the backplane. Another way of making electrical connection to the daughter boards involves using post and box connectors.
Normal forces of 50-100 grams between contacts for making electrical connection between the daughter boards and the backplane are generally needed for reliable electrical connection. With conventional contacts, such normal forces have corresponding insertion forces of approximately 85-115 grams. If there are 300-500 contacts on a daughter board, the total engagement force can exceed 100 pounds.
Some prior systems have provided low insertion forces and subsequent increasing of normal forces by using cams to open, during insertion of the daughter board contacts, backplane contacts that grip the daughter board contacts between opposing portions.